P0378
Timing Reference High Resolution Signal B Intermittent/Erratic Pulses
Encountering the engine check light code P0378 signifies an explicit mechanical or electrical operational breakdown categorized as "Timing Reference High Resolution Signal B Intermittent/Erratic Pulses". Professional scanner tools usually flag this subsystem loop early on.
Driver's Summary
P0378 is triggered when the PCM detects an abnormal condition associated with timing reference high resolution signal b intermittent/erratic pulses. In practice, this fault causes occasional stalling, hesitation on acceleration. This condition is classified as high severity. Prompt diagnosis is essential to prevent cascading damage to related components.
Symptoms
Occasional stalling, hesitation on acceleration
Common Causes
- Loose connector on sensor B
- Wiring harness shorting out intermittently
- Failing sensor B
- Vibration issues
How to Fix
- 1 Secure electrical connector
- 2 Perform wiggle test and repair wire
- 3 Replace sensor B
- 4 Apply dielectric grease
Technical Explanation
The ECM detects code P0378 by continuously monitoring the relevant sensor circuit against calibrated threshold values stored in its non-volatile memory. The PCM monitors crankshaft rotational velocity via the CKP sensor at a resolution of individual tooth gaps on the reluctor ring. A combustion event in each cylinder produces a measurable acceleration spike; its absence or weakness is flagged as a misfire event within a 200-revolution or 1000-revolution test window. The MIL illuminates after the fault is confirmed on two consecutive drive cycles, and the freeze frame data captured at first detection is stored in the PCM's memory for diagnostic reference.
Is It Safe to Drive?
Driving with an active P0378 fault risks accelerating damage to loose connector on sensor b and related components. The longer the fault persists, the more expensive the eventual repair becomes — what starts as a sensor or solenoid issue can escalate to major mechanical failure.
Mechanic's Pro Tip
The most common mistake with P0378 is replacing the sensor without verifying the reference voltage and ground integrity first. Use a scan tool to monitor the sensor's live output; a truly failed sensor shows a stuck, flatlined reading — a sensor that fluctuates but reads slightly off usually indicates a wiring or vacuum issue, not a dead sensor. Always spray electrical contact cleaner on the connector pins before condemning the sensor.
Wiring repair: 100; Sensor: 200 - 400